Multilayer identification cards having optical markings which are contained in an information layer and can be read with the aid of a machine are in extensive use. Among the uses are as credit cards, checks, personal identity cards, season tickets, admission cards and the like. The cards thus serve as payment means, as identity documents, as proof of entitlement to public services, as means for obtaining goods from automatic service-providing machines, etc. In many applications it is required that the information stored on the identifying cards should be capable of being read by a machine and that the cards should be largely incapable of being falsified. Known identifying cards which can be read by a machine do not satisfactorily meet the requirement regarding prevention of falsification.
In a known multilayer credit card, the information that can be read by a machine takes the form of perforations in an information layer. In order to conceal the coded information from the human eye, the information layer is embedded between two protective layers which can be penetrated by infrared light, but through which visible light cannot pass. The information can be read with the aid of infrared light.
It is also known to protect identification cards against falsification by sealing a transparent envelope onto an opaque element which carries information that is printed thereon or applied in some other way, the envelope being made of the same material as the information-carrying element. If an attempt is made to remove the envelope, a refractive profiling, stamped into the surface of the envelope, is destroyed.
Additionally, it is known to store information in the form of holograms or diffraction screens on credit cards.